The present invention relates to a fire-retardant resin composition having excellent mechanical characteristics, flexibility and heat resistance, as well as heat retardancy, and to a wiring material and an optical fiber cord in which said composition is used as a covering material, and other molded parts, in which no crosslinking equipment is necessary when worked.
More specifically, the present invention relates to a fire-retardant resin composition preferably suitable as a covering material for insulated wires, electric cables, and electric cords, which are used for inner and outer wiring of electric/electronic equipment, optical fiber core wires, optical fiber cords, etc., or as a molding material for power source cords, etc., or as a tube or sheet; and to a wiring material and other molded parts in which use is made of the same. More particularly, the present invention relates to a fire-retardant resin composition that is excellent in heat resistance, flexibility and resistance to scarring, which does not need a special equipment, such as a crosslinking equipment, after working, that, in particular, neither exudes heavy metal compounds nor produces a large amount of smoke or harmful gases when discarded, for example, to be buried or burned, and that can be recycled after its use, so that environmental problems may be cleared, and to a wiring material and other molded parts in which use is made of the same.
Insulated wires, cables, and cords, which are used for inner and outer wiring of electric/electronic equipment, optical fiber cores, optical fiber cords, and the like, are required to have various characteristics, including fire retardancy, heat resistance, and mechanical characteristics (e.g. tensile properties and abrasion resistance).
For this reason, as the covering material used for these wiring materials, a polyvinyl chloride (PVC) compound and a polyolefin compound, wherein a halogen-series fire-retardant additive containing bromine atoms or chlorine atoms in the molecule is mixed, have been mainly used.
In some cases, however, when they are discarded or buried without being treated properly, the plasticizer or the heavy metal stabilizer mixed in the covering material is oozed out, or when they are burned, a harmful gas is produced from the halogen compound contained in the covering material. In some cases and in recent years, this problem has become controversial.
Therefore, wiring materials covered with a halogen-free fire-retardant material free from any risk of oozing out of toxic plasticizers or heavy metals, or generation of a halogen-series gas or the like, which involves concern about affecting the environment, are investigated.
Halogen-free fire-retardant materials secure their fire-retardancy by mixing a halogen-free fire-retardant additive in a resin. For example, a material obtained by mixing a large amount of a metal hydrate, such as aluminum hydroxide and magnesium hydroxide, as a fire-retardant additive, in an ethylene-series copolymer, such as an ethylene/1-butene copolymer, an ethylene/propylene copolymer, an ethylene/vinyl acetate copolymer, an ethylene/ethyl acrylate copolymer, and an ethylene/propylene/diene terpolymer, is used as a wiring material.
The standards, for example, of the fire retardancy, the heat resistance, and the mechanical characteristics (e.g. tensile properties and abrasion resistance) required for wiring materials of electric/electronic equipment are stipulated in UL, JIS, etc. In particular, with respect to the fire retardancy, its test method varies depending on the required level (its use to be applied) and the like. Therefore, practically, it is enough for the material to have at least the fire retardancy according to the required level. For example, mention can be made the respective fire-retardancy to pass the vertical flame test (VW-1) stipulated in UL 1581 (Reference Standard for Electrical wires, Cables, and Flexible Cords), or the horizontal test and the inclined test stipulated in JIS C 3005 (rubber/plastic insulated wire test method).
Among these, hitherto, when a halogen-free fire-retardant material is made to have a fire retardancy high enough to pass VW-1 and the inclined test, it is necessary to mix 150 to 200 parts by weight of a metal hydrate, as a fire-retardant additive, in 100 parts by weight of a resin component of an ethylene-series copolymer, such as an ethylene/1-butene copolymer, an ethylene/propylene copolymer, an ethylene/vinyl acetate copolymer, an ethylene/ethyl acrylate copolymer, and an ethylene/propylene/diene terpolymer. As a result, there is a problem that the mechanical characteristics, such as the tensile properties and the abrasion resistance, of the covering material are markedly lowered. To solve this problem, a measure is taken to lower the proportion of the metal hydrate (e.g. about 120 parts by weight of a metal hydrate, as a fire-retardant additive, to 100 parts by weight of a resin), and red phosphorus is added.
Meanwhile, wiring materials that are currently used in electric/electronic equipment, and whose covering material is a polyvinyl chloride compound or a polyolefin compound, wherein a halogen-series fire-retardant additive is mixed, are used by coloring them to be several respective colors, for example, by printing the surface of electric wires, electric cables, and electric cords, for the purpose of distinguishing the types of wiring materials and junctions.
However, halogen-free covering materials having a metal hydrate and red phosphorus mixed therein, to secure both a higher fire retardancy and mechanical characteristics, cannot be printed thereon, or they cannot be arbitrarily colored because of the color of the red phosphorus, so that they have the problem that they cannot give wiring materials that allow the types and junctions to be distinguished easily. Further, phosphorus, which will be released after discarding of the fire-retardant material containing phosphorus, poses also a problem that affects the environment; for example, pollution of water by eutrophication.
Further, wiring materials used in electric/electronic equipment are sometimes required to have a heat resistance of 80 to 105xc2x0 C., or even 125xc2x0 C., while in continuous use.
In that case, such a method is used where the covering material is crosslinked by an electron beam crosslinking method or a chemical crosslinking method, in order to render the wiring material highly heat resistant.
However, while the crosslinked wiring material has improved the heat resistance of the covering material, it is impossible to remelt it. Therefore it is difficult to use said material again, making the recylability thereof poor. For example, when a metal used as a conductor is recovered, the covering material has, for example, to be burned in many cases, which means that the above environmental problem involving the conventional halogen- or phosphorus-containing covering material cannot be avoided. Further, a special equipment, such as an electron beam crosslinking equipment or a chemical crosslinking equipment, has to be provided. This increases the installation cost and the cost of the resultant electrical wire, thereby degrading the general-purpose properties.
On the other hand, as a technique wherein a wiring material having a heat resistance, on the order of 80xc2x0 C. to 105xc2x0 C., is realized without carrying out such crosslinking, there is a technique wherein a resin having a high melting point, such as a polypropylene-series resin, is used. However, although such a resin has good heat resistance, the flexibility is poor, and when the wiring material covered with such a resin is bent, a phenomenon is observed that the surface is whitened.
This whitening phenomenon is not observed in wiring materials currently used in electric/electronic equipment and covered with a polyvinyl chloride compound. On the other hand, in the case of wiring materials covered with a halogen-free fire-retardant material wherein a large mount of a metal hydroxide is mixed, this whitening phenomenon is conspicuous regardless of whether they have been subjected to the crosslinking process or not. Thus, to use the current halogen-free fire-retardant material, which is whitened when bent, for wiring materials, further improvement has been required.
Since the service temperature of a wiring material covered with a polyvinyl chloride compound is generally on the order of 80xc2x0 C. or 105xc2x0 C. as a UL Standard""s Temperature, a halogen-free fire-retardant material for use as a replacement for the wiring material is also required to have that heat resistance. Specifically, since, for a heat resistance of UL 80xc2x0 C., for example, the heat deformation test and the heat aging test in an atmosphere at 121xc2x0 C. are required, and further, for a heat resistance of UL 105xc2x0 C., for example, the heat deformation test and the heat aging test in an atmosphere at 136xc2x0 C. are required, the halogen-free fire-retardant material, as a replacement, is required to not melt at at least 121xc2x0 C., preferably at 136xc2x0 C.
In addition, molded parts, such as power source plugs, have the similar problems as the above, and the development of molded parts has been desired, which have heat resistance, flexibility, and fire retardancy, which can be recycled, and which can be remolded.
Wiring for electronic equipment that is used in electronic equipments is required to satisfy requirements stipulated under a particularly severe vertical fire-retardancy standard (UL1581 VW-1) of UL Standard. However, even if a covering material is constituted with the above-described resin having a high melting point, such as a polypropylene resin, to which a metal hydrate is added in a large amount, it is difficult to largely improve the fire-retardancy of the covering material, and therefore, it does not satisfy the requirements stipulated under the vertical fire-retardancy standard that is a severe fire-retardancy standard.
A covering material of an electrical wire used for household electric appliances is also required to satisfy dynamic properties stipulated, e.g., under UL Standard, more specifically, required to have an elongation of 100% and a tensile strength of 10.3 MPa or more. In particular, a covering material of a power code is required to further have a good flexibility because power codes are shipped in the bundled state.
On the other hand, a tube, an electrical wire part, and a sheet other than the electrical wire, and further a molded part such as a power plug are required to be similarly desirable in heating deformation characteristic, fire-retardancy, dynamic strength, and flexibility. In particular, a sheet or tube for use in protection or connection of an electrical wire or for use as a building material, is required to have a good surface flexibility and a high resistance against damage (scarring); however, a conventional halogen-free material fails to simultaneously satisfy these characteristics.
An object of the present invention is to provide a fire-retardant resin composition that solves the above problems, that is excellent in fire retardancy, heat resistance, and mechanical characteristics, and that neither exudes heavy metal compounds nor produces a large amount of smoke or harmful gases when discarded, for example, to be buried or burned, so that recent environmental problems may be cleared. Another object of the present invention is to provide a molded article that solves the above problems, that is excellent in fire retardancy, heat resistance, and mechanical characteristics, and that neither exudes heavy metal compounds nor produces a large amount of smoke or harmful gases when discarded, for example, to be buried or burned, so that recent environmental problems may be cleared. Further object of the present invention is to provide a fire-retardant resin composition having, in particular, both the high fire-retardancy and flexibility, that gives a covering material that can be remelted, to allow it to be reused; that is not whitened when bent, and that is not easily scarred, while satisfying the above characteristics. Still another object of the present invention is to provide a wiring material, an optical fiber core, an optical fiber cord, and other molded parts wherein said composition is used, respectively.
Other and further objects, features, and advantages of the invention will appear more fully from the following description, taken in connection with the accompanying drawings.